1. Field of the Invention
The present invention relates to a rolling bearing manufacturing apparatus and method and, in particular, to a technology which works a groove in a rolling bearing in order to provide a substantially constant internal clearance after the rolling bearing is assembled, thereby enhancing an efficiency of a rolling bearing assembling operation.
2. Description of the Related Prior Art
In FIG. 5, there is shown a single row ball bearing 1 which is an example of a conventional rolling bearing. The single row ball bearing 1 comprises an outer race 2, an inner race 3, and a plurality of rolling elements (for example, balls) 4. The bearing 1 is assembled in such a manner that a predetermined amount of clearance is provided between the respective raceway grooves 2a, 3a of the outer and inner races 2, 3 and their associated rolling elements 4.
Conventionally, in a grinding process for grinding the above-mentioned raceway grooves of the outer and inner races, there are previously set target dimensions respectively for the raceway diameters with respect to their associated outer race raceway groove and inner race raceway groove and, while controlling the dimensions of the outer and inner race raceway diameters independently of each other, the raceway grooves of the outer and inner races are worked separately. That is, the raceway grooves are ground independently of each other with no mutual relation between the outer and inner races 2 and 3.
That is, when grinding the outer race raceway groove 2a, the quality of the grinding operation is controlled such that the raceway diameter Da of the outer race raceway groove 2a does not deviate from the range between an upper limit value Damax and a lower limit value Damin determined with respect to a standard dimension Dao.
In this case, the raceway diameter Da of the outer race raceway groove 2a varies as shown in FIG. 6(a) as the number of outer races 2 actually manufactured increases. Here, variations in a rising portion shown by an arrow a are variations in the dimension of the outer race raceway diameter caused by the thermal deformation of a grinding wheel, whereas small variations respectively shown by an arrow b are variations in the dimension of the outer race raceway diameter caused by the dressing of the grinding wheel. Also, as shown by an arrow c, if the value of the raceway diameter Da reaches the upper limit value Damax, then dimension feedback is carried out by means of a post-gauging operation or a dimension adjustment is made by an operator, so that the value of the raceway diameter Da is returned to the standard dimension Dao.
On the other hand, when grinding the inner race raceway groove 3a, similarly to the above grinding operation of the outer race raceway groove 2a, the quality of the grinding operation is controlled such that the raceway diameter Db of the inner race raceway groove 3a does not deviate from the range between an upper limit value Dbmax and a lower limit value Dbmin determined with respect to a standard dimension Dbo.
In this case, the raceway diameter Db of the inner race raceway groove 3a varies as shown in FIG. 6(b) with an increase in the number of inner races 3 actually manufactured. However, since the size of a grinding wheel and a mechanical structure employed in the present grinding operation are different from the former grinding operation, the variation pattern of the raceway diameter Db of the inner race raceway groove 3b is considerably different in the variation cycle and the like from the variation pattern of the raceway diameter Da of the outer race raceway groove 2a shown in FIG. 6(a).
After the above grinding operation of the respective raceway grooves, generally, in order to enhance the degree of the roughened surfaces of the groove surfaces, a substantially predetermined amount of minute margin is removed from the groove surfaces by a superfinishing machine. Next, in an assembling step, out of the outer races 2 and inner races 3 which have been manufactured separately, there are extracted an outer race 2 and an inner race 3 at random, the respective raceway diameters of the thus extracted outer and inner races are measured, a plurality of rolling elements 4 each having a proper outside diameter Dc are selected on the basis of the thus measured raceway diameters in such a manner that an internal clearance in the assembled body can be set within a specified range, and the thus selected rolling elements 4 are respectively assembled with the outer race 2 and inner race 3.
As the rolling element 4, there are previously prepared a plurality of rolling elements having two or more ranks of outside diameters such as .+-.0, .+-.1 .mu.m, .+-.2 .mu.m, .+-.3 .mu.m, and .+-.4 .mu.m in nominal dimensions, and a plurality of rolling elements each having a proper rank of outside diameter are selected out of the prepared rolling elements.
For example, when a raceway diameter difference between the outer race raceway groove 2a and the inner race raceway groove 3a is larger by 2 .mu.m than the standard dimension (that is, the difference is +.+-.2 .mu.m with respect to the standard dimension), there is selected a rolling element 4 having an outside dimension Dc which is smaller by 1 .mu.m than the standard dimension (that is, -1 .mu.m with respect to the standard dimension).
On the other hand, when the raceway diameter difference between the outer race raceway groove 2a and the inner race raceway groove 3a is -8 .mu.m with respect to the standard dimension, there is selected a rolling element 4 having an outside dimension Dc which is +4 .mu.m with respect to the standard dimension.
By the way, when there have been collected 10,000 pieces of data on the deviation amounts of the raceway diameters Da of the outer race raceway grooves 2a from the standard dimension Dao as well as on the deviation amounts of the raceway diameters Db of the outer race raceway grooves 3a from the standard dimension Dbo, it has been found that they are distributed in such a manner as shown by a histogram in FIG. 7. That is, according to FIG. 7, the raceway diameter of the outer race 2 has a peak at a value of approx. +17 .mu.m, whereas the raceway diameter of the inner race 3 has a peak at a value of approx. +2 .mu.m. In other words, the outside diameters of the rolling elements are set such that, when the outside diameters provide such peak dimensions, there can be formed an ideal clearance (that is, a clearance dimension regarded as a standard dimension).
If it is assumed that the actual dimension of the clearance is expressed as hr and the standard dimension of the clearance is expressed as hro, then the relation between the raceway diameters of the respective outer and inner races, rolling element outside diameters and clearance dimensions can be expressed by the following equation: that is, EQU (hr-Hro)=(Da-Dao)-(Db-Dbo)-2(Dc-Dco),
where Dco expresses a rolling element outside diameter dimension regarded as a standard dimension.
Now, assuming that a standard clearance dimension hro is 15.+-.1 .mu.m and the adjusted dimensions of prepared rolling element outside diameters are .+-.0 .mu.m, .+-.1 .mu.m, .+-.2 .mu.m, .+-.3 .mu.m, and .+-.4 .mu.m, that is, 9 ranks, for example, when the raceway diameter dimension difference of the outer races 2 is +17 .mu.m and the raceway diameter dimension difference of the inner races 3 is +2 .mu.m, if there is selected a rolling element 4 having an adjusted dimension of 0 .mu.m, then a clearance dimension can be set as +15 .mu.m which falls under the dimension range of the standard clearance.
However, during actual manufacture, there can occur a case where an outer race 2, in which the raceway diameter Da of the outer race raceway groove 2a is deviated greatly toward the + side with respect to the standard diameter Dao, and an inner race 2, in which the raceway diameter Db of the outer race raceway groove 3a is deviated greatly toward the - side with respect to the standard diameter Dbo, are combined together. For example, when the raceway diameter dimension difference of the outer race 2 is +24 .mu.m and the raceway diameter dimension difference of inner outer race 3 is -6 .mu.m, even if there is selected a rolling element 4 having the largest rank of outside diameter, that is, +4 .mu.m, the clearance dimension becomes 24-(-6)-2.times.4=22 .mu.m, which does not fall under the standard clearance dimension range (15.+-.1 .mu.m).
Therefore, in order to make the clearance dimension fall under the allowable range, it is necessary to prepare separately a rolling element 4 whose deviation amount with respect to the standard dimension is -7 or -8 .mu.m, or it is necessary to change the combination of the currently selected outer race 2 and inner race 3.
However, in the former case, it is necessary to expand the range of classification of the outside diameters Dc of the rolling elements. This not only takes time and labor to manufacture the rolling elements as well as measure and classify the outside diameter dimensions thereof, but also complicates an operation to select proper rolling elements before assembling the rolling elements together with outer and inner races.
Also, in the latter case, one of the inner and outer races once combined together must be replaced a new one, with the result that an operation to assemble the outer and inner races is inevitably made troublesome.
That is, in the above-mentioned conventional rolling bearing manufacturing method or apparatus, since the outer and inner races separately manufactured are combined together at random, it is difficult that the inner and outer races, which vary in dimension in a time series manner, are combined with the rolling elements with high precision.